Onsager bands”

An increase of the photocurrent at energies less than 2 eV was observed [151,152] unlike the previous result. This was attributed to the localized impurity ionization up to 0.8 eV below the conduction band. The crystals are considered as model systems for the one and three-dimensional versions of Onsager s theory of germinate recombination. 

Delay et al (Ref 12) detd IR absorption spectra in the range 3 to l9u and from the intensities of the bands concluded that the sym form was more abundant in the azides of Ag, Cu, Hg Na but the reverse was true for the azides of Pb Tl. Gray Wad ding ton (Ref 18) stated th at TlNj crysts are isomor-phous with those of Na Rb azides. The elec conductivity of TIN, is 5.9 x 10 s mho at 275° (Ref 18). Brouty (Ref 10) detd the mean activity coefficient of TIN, by EMF+ measurements and calcd ionic radii of Ti Nj. Conductivity measurements by Brouty (Ref 11) did not agree with Onsager s theory deviations were found at very high dilutions. An electro-chem cell used by Suzuki (Ref 16) gave a Ap1 29S° value of 59.17 kcal/mol for... 

The solvatochromic shift is the displacement of an absorption or emission band in different solvents. Figure 3.49 shows examples of such shifts, the transition energy being linear with the Onsager polarity function f D). The... 

Figure 3.49 Examples of solvatochromic plots of absorption spectra, (a) The first absorption band of 4-nitroaniline (charge transfer band), (b) The first absorption band of acetone (n-n band). The ordinates are in units of 103 cm, measured at the band maximum the abcissa are in units of Onsager solvent polarity function f(D)...

Figure 3.50 Outline of the solvatochromic shifts of different absorption bands of the same molecule (e.g. 4-aminobenzophenone). In this case the first transition corresponds to a much larger change in dipole moment, v wavenumber in 103 cm-1 f(D) Onsager polarity function A absorbance...

Figure 3.57 Solvatochromic plot of the first absorption band of a betaine dye. The transition corresponds to a CT from 0 to the aromatic system. Triangles are protic solvents. E is in kcal moE1 and f(D) is the Onsager function...

In water, at ordinary concentrations, the hydrogen chloride is practically all present as the hydrated ions. The infrared absorption bands characteristic of HCl, and shown by the liquid hydride and its solutions in nonionizing solvents do not appear in the aqueous solutions.451 In dilute solutions, the conductivities agree with the Debye-Huckel-Onsager formula. 

The spectral position of absorption and fluorescence are influenced by the dielectric properties of the medium in which observations are made. Figure 5 shows that the vapour phase 0-0 bands in absorption and fluorescence of a molecule are identical, whereas in solution with solvent of static dielectric constant e, refractive index n, the bands are no longer coincident. The differences can be rationalized as follows. From Onsager theory, a solute molecule of dipole moment ju in a spherical cavity of radius a polarizes the dielectric of the solvent, producing a reaction field. This is given for the ground-state of the solute molecule (of dipole moment iiq), by (22). Upon excitation, and invoking the Franck-Condon principle, the electronic excitation is much more rapid than the dielectric relaxation time of... 

The importance of light absorption to directly populate the triplet state in the presence of heavy atoms [(10.271)] and the effect of heavy atoms on the phosphorescence of acenaphthylene [(10.27m)] are easily ruled out. No new absorption bands or increased band intensities are noted in the presence of heavy atoms. Since no phosphorescence is observed, even at low temperature, there cannot be an important effect on this process. A heavy-atom effect on the partitioning of reactions (10.27g,h) and (10.27k) is eliminated by the data of Hartmann, Hartmann, and Schenck in their study of solvent effects on the photosensitized photolysis of acenaphthylene. The influence of a number of solvents was described with the use of Kirkwood-Onsager solvent parameters (an empirical method for the correlation of reaction rate with the ability of the solvent to stabilize the change in dipole moment in proceeding to the transition state). A linear plot of log(fra/u/cw) vs. the expression [(Z) — 1)/(2Z) -f- where D is the dielectric constant, p is... 

The intensities of polarised Raman bands of binary mixtures of many solvents have been studied over a wide concentration range by Fini et The scattering coefficient increases, in most cases linearly, with the refractive index of the mixture and is in good agreement with a theoretical formula, derived from Onsager s theory of dielectric polarisa-tion. For those systems which do not conform to the theory specific intermolecular interactions are probable. 

McRae s equation, which uses the Onsager dielectric functions, has been used to interpret the solvatochromism of a number of coordination compounds. Meyer and one of us have also used Kirkwood s approach, which is simpler since it neglects dispersion forces. Lippert s method is used for species in which absorption and emission data are available for the same excited state when the difference between absorption and emission energies is known a number of terms in the equations will cancel, and it is then relatively simple to obtain the ground- and excited-state dipole moments. This method is not usually applicable for coordination complexes as, if emission is observed, the emitting state is usually different from the main absorption band, e.g., in many cases absorption is to a singlet state and emission is from the corresponding triplet. 

Total absorption coefficient (aex + %) of DCH obtained by Kra-mers-Kronig analysis of 8 K reflection data. The broken portion of the spectrum reflects transitions within the carbazole chro-mophore. ab is the profile of the ionizing transition the broken portion reflects sensitised carrier generation via excitation of the sidegroup (49). Eg indicates the band gap measured by electroreflection at 2 K (from ref.(36)). The free carrier yield is (() = 4>escab(otb + o ex) 1 where <() sc g the Onsager escape probability in ID. 

The influence of the central metal ion on the TPA properties—as well as on the second-order NLO response—of push-pull porphyrins has been investigated by Ray et alP by employing the ZINDO/Correction Vector (ZINDO/CV) method combined with the Onsager Self-Consistent Reaction Field (SCRF) method to account for solvent effects. Metalloporphyrins with strong CT bands are shown to exhibit an increase of both NLO responses by one order of magnitude with respect to the porphyrin without metal. These NLO responses further increase by at least one or two orders of magnitude when going from the monomer to the dimer and trimer. 

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